Sweep or pulse generator



Dec. 17,1946. w. D. HERSHBERGER 42,412,682

SWEEP OR PULSE GENERATOR 4Filed July s1, 1942 2 sheets-sheet 1 uw m Dec. 17,1946. w.- D. HERSHBERGER 2,412532 SWEEP 0R PULSE GENERATOR Filed July 51, 1942 2 sheets-sheet 2 "upf T it T nventor Patented Dec. 17, 1946 naar 2,412,682 Y sWEEP on PULSE GENERATOR William nnershberger, Haddonfiela, N. J., as-

signor to Radio Corpora poration of Delaware tionof America, a cor- Application July s1, 1942, serial 510,453,088 v Claims.

My invention relates to cathode ray deflecting circuits and particularly to deecting circuits for producing an exponential deection to be used, for example, in a radio pulse-echo system for measuring the angle formed by a line from an aircraft to a ship or other target and a perpendicular line from the aircraft to earth.

'Ihe pi'esent invention is an improvement on the deflecting circuit of the pulse-echo system. for measuring angles described in application Serial No. 452,989, led July 31, 1942, in the name of Irving Wolff.

An object of the invention is to provide an improved delecting circuit for producing an exponential deection of a cathode ray.

A further object of the invention is to provide an improved cathode ray deecting circuit for producing an exponential deection without defocusing the cathode ray during deflection.

The invention will be described for the purpose of illustration as applied to a radio pulse-echo system which radiates a signal downward and forward from an aircraft whereby reflections that are a measure of altitude will be received from the earth directly below the plane while other reflections will be received from the target ahead. Since the rst occurring reection will be a measure-of the distance A perpendicular to the earth, the angle 0 between this perpendicular line and the line from the aircraft to the target can be determined when the distance T1 to the target is also known. The latter distance T1 is shown by .a later occurring reiiection from the target. From the fact thatthe distance to the target divided by the altitude is the secant of the angle 6, the angle 0 may be calculated. As described in the above-mentioned Woli application, however, the apparatus is so designed that the angle 0 may be read directly on scale without the necessity of any calculations.

The present invention provides a precise exponential sweep or timing voltage that can be applied directly to a pair of delecting plates of a cathode ray tube without defocusing the cathode ray. In a preferred embodiment of the invention two capacitors are connected in the plate and cathode circuits, respectively, of two vacuum `tubes which are made periodically current conducting to cause sawtooth voltages of opposite polarities to appear across the two capacitors. These sawtooth voltages are applied directly to the two plates, respectively, of the pair of deilecting plates in the cathode ray tube. The vacuum tube that has a capacitor in its cathode circuit preferably has a screen grid electrode which is 2 driven positive by a voltage pulse during the period this tube is made conductive. y

The invention will be better understood from the Yfollowing 'description taken in connection with thel accompanying drawings in which Fig. 1 is a block and circuit diagram of apparatus embodying my invention, Fig. 2 is a circuit diagram of another embodiment of my invention, and Fig. 3 is a view of the end or the cathode ray tube in Fig. 1. In the severalgures like parts are indicated by similar reference characters. f

Referring to Fig. 1 of the drawings, a high frequency radio transmitter I2 is keyed by means of a pulse keyer I3' and a keying pulse generator ill to radiate short radio pulses downward and forward from a suitable directive antenna system iii. The transmitter pulses are also supplied over a conductor 20 to a receiver 22 to function as initial or time reference pulses. The keying pulses preferably are applied to the keyer I3 through a delay circuit I5. The antenna system I6 may be two dipoles in parabolic reflectors which radiate in overlapping left-hand and right-hand radiation patterns, only one dipole and reflector being shown in the drawings. The two dipoles are connected alternately to the transmitter I2 by means of suitable left-right switching means II driven by a motor I8. The transmitted pulses may occur at the rate of 3500 per second and have a duration of 0.3 micro-second; the switching from left to right may occur at the rate of per second. These values are given merely by way of example.

The reflected pulses are picked up by a suitable antenna such as a dipole 2| and supplied to the receiver 22 which ampliiies and demodulates them. They are further amplied by an amplifier 23 and applied through switch arms 2li and 25 to a pair of deilecting plates 21 and 21a of a cathode ray tube 29. A resistor 28 with a grounded midpoint is connected across the deecting plates 21 and 21a. The switch arms 24 and 25 are `operated synchronously with the leftright antenna switching whereby the cathode ray of tube 29 is deected to give a left indication when the antenna radiation is toward the left and to give a right indication when the antenna radiation is toward the right. The alternate closing of switches 24 and 25 is effectedV by means of a suitable left-right switching mechanism driven by the motor I8. The cathode ray tube 29 may be of conventional design and is provided with a second pair of deflecting plates 3| and 3Ia positioned at right angles to the other pair of plates. An exponential sweep or timing may be described as a non-linear and is applied over voltage is applied to the plates 3l and Sla to deilect the cathode ray vertically at a repetition rate of 3500 sweeps per second in the example being described.

My improved push-pull deecting circuit is especially adapted for supplying a suitable exponential voltage for use above-described type. It comprises a variable capacitor 33 associated with a plate loaded tube 33 and a variable capacitor 36 associated with a cathode loaded tube 31; The tube 34 functions as a discharge tube for capacitor 33 and may be a screen grid tube which is Ybiased substantially to plate current cutoff by means of grid leak biasing provided by a resistor 39 and a capacitor 4l in the control grid circuit, for example. The grid circuit of tube 34 preferably includes a low resistance resistor for reducing parasitic oscillations. Capacitor 33 receives a charge from a voltage source 42 through thetube 34 upon the application of a 'pulse P to the control grid 40 `of tube `3ft from the pulse generator 1'4. The output 'circuit of source 42 includes the usual bleeder resistorS'l and lter 'capacitor 82. Thepuls'es P are applied from a 'generator I4 through a condi'ictor 44, an 'amplifier tube 46, an 'amplifier tube 41 and atra'nsforrner 48 which has a secondary winding 3 that is damped by a shunting resistor.

The cl'iargihg path for 'capacitor 33 'may be traced'frbm the positive tfrm'in'al of voltage source 42 through a conductor 35 and a section of jthe volta/ge divider V58 and lits bypass capacitor1 33 'to ground, through "round tov the lower terminal of 'capacitor 33, and through the capacitor 33 and the plate-'cathode irnpeda'nce 'of tubes 34 to the rnegative .terminal of the 'voltage source 42. At the nd of the pulse Pthe capacitor 33 'discharges through a 'path that ly be traced from vthe up- 'perl terminal 'of capacitor 33 throughjthe Vresistor "E3 ofV tube 34, the conductor 35, a section of voltage divider v58 and its bypass capalcito` 3B to ground, and through 'ground 't'o the lower terminalo'f capacitor 33. v

It should be not'd that the Acaps'alcitor 33 always 'discharges 'completely 'to bring 'its upper terminal l(and also the deflectin'g plate 31) to the 'centering -potential 'at the 'tap l1. It is 'at the 'vend of the discharge period that the cathode ray is "at the upper n'dof 'its sweep. It lfollows that changing 'the amplitude 'of Vvoltage 'from soul-'ce 4,2 does hot affect the centering jat 'this end 'of the V'sv'veep so far as apaltor 33 `i`s concerned. The same is true with respect to capacitor '33 as will immediately be apparent. The lower Iterminal ofvj'capa'citor ,'33 may be connected to the negative terminal of voltag'e'source '112 instead of to ground,'if desired. Y The 'sweep voltage appearmgacross capacitor 33 is shown at 5I. It has a Awave shape that lsavltmth 4wave shape, the useful 'deecting portion of the `sawtooth'being exponential, 'that is, being fben't over in accordance with the discharging of 'capaci-tor 133 through resistor 43 at anfe'xponential rate. Preferably 4during each pulse P the Acapacitor 33 is fully charged andat the Afend of eacnelischarging period it is completely discharged. The voltagewave 5I is applied` over a conductor 52 directly to the deflecting plate Y3| The sweep voltage appearing "across Vcapacitor 33 is shown jat 53. It has the same wave shape as the voltagewave 5| but is of opposite polarity r 'ajconductor 54 directly 5to the ydeflecting plate 3121. The Vdesired A'polarity of the wave 53 is obtained by connecting the capaciin apparatus of the @5 vandV 53, and preferably is secondary tor 33 in the cathode circuit of tube 31 rather than in the plate circuit. Capacitor 33 receives its charge from a voltage supply 55 through the anode-cathode impedance of tube 31 when said impedance is lowered by the occurrence of a voltage pulse P as will be explained below. The output 'circuit of source 56 includes the usual bleeder resistoi` 33 and lter capacitor 33. The tube 31, like the tube 33, is normally biased to substantially cut-off by means of vgrid circuit elements provided with a parasitic reducing resistor 1. The path of the charging Vcurrent may be traced from the positive terminal of source 36 through the tube 31, the capacitor 33 to ground,'from ground through a voltage divider resistor 58 and a bypass capacitor 55 to a centering tap l0 located thereon, and through a conductor 53 to the other terminal of the source 53. At the end of a pulse P the capacitor 33 c li'schar'ges through a cathode resis-tor El, the conductor y59 and the portion of the volt- 'age divider 53 located between the centering tap li) and ground. Here again the capacitor discharges completely Ybringing the upper terminal of capacitor 33 to the centering 'potential rat tap i3 whereby the upper end position of the cathode ray sweep is independent of changes in the voltage amplitude of source 5B. Y l

The centering circuit disclosed lin this application is described and claimed in copendingapplication Serial No. 455,409, led'August 20, 1942, in the name of Max H. Mesner, and-entitled Exponential deflecting and `centering circuits.

In the particular equipn'len' being described, the time constant of the sweep circuit 33-43 (or circuit 33-3i), when set to measure the maximum altitude, such as l210,000 feet, is about one-fifth the period of the vertical sweep, this being the condition for maximum resistance and maximum capacitance in the sweep circuit and for the least amount of discharge Of the Capacitor 33 (and of capacitor 36) at the end 'of the sweep. Even for this condition capacitors 33 "and 33 are substantially completely discharged; specically, if the charging voltag'erfro'm source '42 is'2000 volts, the capacitor 1'3 3discharg`es to '1 for 8 volts which is such 4'a small percentage vof the 'charging voltage 'that the failure to discharge to Zero voltsdoes not affect the'operation. y

'Referring 'again to the 'charging 'period forcapa'iito'r 36, the VVplate-cathode impedancejo'f tube 31`is lowered "during theV occurrenceofeach pulse P 'by applying these pulses ysimultaneously toits 'control grid 32 and to 'its screen 'grid :33. 'lIhe control 'grid 'B2 vreceivesY its pulse Vthrough the 8 :of transformer '48 while Athe `screen grid V63 receives its pulse thro-ugh Vvan amplifier tube 6d 'and a transformer 63, the ltube 34 being coupled to the anode circuit of Aam'plier-tube I6. The secondary Vt and the vsecondary of `transforn'ier-GE are shunted by vdamping resistors. It will be noted that the voltage pulses are applied to thegrids-52 `and 63 with respect vt'o the cathode 31 of Itube 31, 'not with respect `to ground. As la result, it "is possible to-'operatetube 31'=wi'thigood gain wherebyno diflicultyfis encounteredin driving the Ttube 31 vfronti its 'normal -ahodecurrent lcut-olf condition t'o low anode-cathode lirripetiance Iby a pulse-Pof reasonable amplitude. The reason for applying the fv'oltag'e pulses to the screen grid '63 44as well as tothe control grid l:(52 is that the cathode ,61swingspositiveaboveground potential when capacitor 36 receives itscha'rge. -By applying-'a pulse "to the screenfgrid fat'this time, it is brought to the proper positive potenentre ltap 69 on a potentiometer resistor 'H which has its ends connected to opposite sides of a grounded point on the voltage divider 58.A

The voltage sources d2 and 53Y are rectifierlfilter units supplied with power from an A.C. line through a voltage control unit 'l2 such as a Variac and through a transformer 13. Adjustment of the tap marked Vertical size adjusts the .amplitude of the vertical sweep. The primary Winding of transformer 'I3 has a midtap and an end tap, indicated by the legends Angle and Set-up, respectively. By moving a switch arm 14 from its set-up position to its angle position the voltage supplied by the units 42 and 56 is doubled and the amplitude of the vertical .sweep is doubled.

The Variable capacitors 33 and 33 are mechanically coupled to a dial pointer 'IS associated with an altitude scale '11. Thus the pointer 'F6 rotates when a knob 18 is rotated to change the capacity Vof capacitors 33 and 36 for the purpose of set up and for obtaining altitude as explained below. In the example being described, each of the capacitors 33 and 38 has a capacity range from 150 mmf. to 550 mmf.

VThe procedure in setting up and reading the altitude and angle scales, is as follows:

(1) The switch 'lli is thrownv to the set up position shown in the drawings so that one-half full deiiection voltage is applied from capacitors 33 and 36 to the vertical deiiecting plates 3l and 31a.

(2) The end of the vertical sweep or cathode ray trace is brought opposite the 90 degree mark at the top of the angle scale by adjusting the centering tap I on voltage divider 58.

(3) The initial or time reference pulse I. P. (Fig. 3) is then brought opposite the Zero mark at the bottom of the angle scale by means of the vertical size tap. With my deflecting circuit it is not necessary to re-center to keep the end of the trace opposite the 9G degree mark since the capacitors 33 and 35 always discharge to the centering potentials whereby the upper end of the trace remains Xed.

(4) The altitude echo pulse A (Fig 3) is next brought opposite the 60 degree mark, which is at the mid-point on the angle scale, by rotating the knob 'I8 and thereby adjusting the rate of discharge of capacitors 33 and 38. This is the adjustment that brings the Voltage across capacitors 33 and 38 to one-half the initial voltage value and the indication then occurs at the 60 degree mark'. Rotation of the knob 'i8 also rotates the pointer IE of the altitude scale from which the altitude may now be read.

(5) The switch M is next moved to its angle measuring position putting the full sweep voltage on the vertical deecting plates whereby the length of the vertical sweep is doubled. This brings the altitude pulse A to the zero mark on the angle scale. As noted above, the upper end of theV sweep trace does notchange its position and no further centering is required. The initial pulse moves off the scale. Y

(6) The angle 0 for a target thai-,reflects a pulse T1 (Fig. 3) may now beread directly from the point on the angle scale opposite thepulse T1. The reason that the angle 0 and the altitude can-be determined in the manner described above has been more fully described in the above-identied Wolff application b-ut need not be repeated here.

From the foregoing it will be seen that altitude may be read from the dial 'Il andthe angle 0 from the scale on the cathode ray tube 29. At the same time the indications reveal whether the Y target sought is to the right or left of line of night of the aircraft. This is accomplished by the alternate antenna switching previously described which is done at a superflioker rate. A visual comparison between the amplitudes of the pulses corresponding to the echoes from the left and right is made to determine the direction in which the target lies.

It will also be apparent that a precise -exponential sweep deflection is provided without deiocusing the cathode ray of the indicator Stube. The precision of the sweep is insured by the fact that the voltages appearing across capacitors 33 and 3% are applied directly to the deiiecting plates.

In the drawings the values of various circuit elements have been indicated, merely by way of example, in ohms and microfarads.

In Fig. 2 the vertical sweep circuit is similar to that of Fig. l but the negative terminals of the voltage sources l2 and 53 are grounded and the centering is accomplished by means of adeiiectng coil 86 supplied with direct current from a battery or other suitable source 81. The upper end of the vertical sweep at the end of tube 29 is brought opposite the 90 degree mark by adjusting a centering tap 88. l

A minor difference between Figs. 1 and 2 is that in Fig. 2 the tube 34 is biased substantially to 'cutoff by cathode biasing instead of by grid. leak biasing. "A more important diierence is vthat in Fig. 2 the screen grid 53 and the control grid 32 of tube 3l have the pulses P applied thereto from the same amplifier tube 64 instead of from diierent amplifier tubes.

It will be understood that the circuit of Fig. 2 operates the same as the circuit of Fig. 1 except -as to the diierences mentioned above.

I claim as my invention:

1. A cathode ray deflecting circuit comprising an electric discharge tube having a control grid circuit and an anode circuit, a capacitor and an anode resistor located in said anode circuit, means for charging said capacitor through said tube in response to the application of lperiodically recurring pulses to said control grid circuit, means for discharging said capacitor through said resistor, a second electric discharge .tube having a control grid, an anode and a cathode, a capacitor connected between said cathode and a point that is negative with respect to said cathode, means for charging said last capacitor through said second tube in response to the application of said pulses to the said grid of said second tube, a cathode resistor for said second tube, and means for discharging said last capacitor 'through said cathode resistor whereby sawtooth deiiecting voltages of opposite polarity appear across said capacitors.

2. A cathode ray deecting circuit comprising an electric discharge tube having a control grid circuit and an anode circuit, .a capaci-tor located in said anode circuit, means for alternately substantially completely charging said capacitor and substantially completely discharging said capacitor in response to lthe application of periodically recurring pulses to said control grid circuit, a second electric discharge tube having a control grid, a screen grid, an anode and a cathode, means for so applying said pulses to said last named grids as to drive them positive with respect to the cathode of said second tube, and a capacitor connected between said cathode and a point that is negative with respect to said cathode, and means for alternately substantially completely charging said last capacitor and substantially completely ydischarging said last capacitor inresponse to the application of said pulses to the said grids of said second tube.

3. A cathode ray deflecting circuit comprising an electric discharge tube having a control grid circuit and an anode circuit, a capacitor located in said anode circuit, means for alternately substantially completely charging said capaci-tor and substantially completely discharging said capacitor in response to the application of periodically recurring pulses to said control grid circuit, a

ysecond electric discharge tube having a control grid, a screen grid, an anode and a cathode, means for so applying said pulses to said last named grids as to drive them positive with respect to the cathode of said second tube, and a capacitor connected between said cathode and a point .that is negative with respect to said cathode, means for alternately substantially com- .pletely charging said last capacitor and substantially completely discharging said last capacitor in response to the application of sai-d pulses to the said grids of said second tube, a cathode ray tube having a pair of deflecting plates, and means for applying the voltages appearing across said capacitors to said deflecting plates in push-pull relation.

4. A cathode ray deilecting circuit comprising an electric discharge tube having a control grid circuit and an anode circuit, a capacitor and an anode resistor located in said anode circuit, means for charging said capacitor through said tube in response to the application of periodically recurring pulses .to said control grid circuit, means for discharging said capacitor through said resistor, a second electric discharge tube having a control grid, a screen grid, an anode and a cathode, means for so applying said pulses to said last named grids as lto vdrive them positive with respect to the cathode of said second tube, a capacitor connected between said cathode and a point that is negative with respect to said cathode, means for charging said last capacitor through said second tube in response to the application of said pulses to the said grids of said second tube, a cathode resistor for said second tube, and means for discharging said last capacitor through said cathode resistor.

5. A cathode ray deflecting circuit comprising an electric discharge tube having la control grid circuit vand an anode circuit; .a capacitor and an anode resistor located in said anode circuit, means for charging said capacitor through said tube in response to the application of periodically recurring pulsesto said control grid circuits, means for -discharging said capacitor through said resistor, a second electric discharge tube having a control grid, a screen grid, an anode and a cathode, means for so applying said pulses to said last named grids as to drive them positive with respect to the cathode of said second tube, a capacitor connected between said cathode and a point that is negative with respect to said cathode, means for charging said last capacitor through said second tube in response to the application of said -pulses to the said grids of said second tube, a cathode resistor for said second tube, means for discharging said last capacitor through said cathode resistor whereby sawtooth deflecting voltages of opposite polarity appear across said capacitors, a cathode ray tube havying a pair of delecting plates, and means for applying said deflecting voltages directly .to said deecting plates.

WILLIAM D. HERSHBERGER. 

